1. Field of the Invention
The present invention relates to semiconductor devices, and in particular to a semiconductor device provided with a projecting electrode.
2. Description of Related Art
In recent years, there has been a strong demand for a further downsizing of semiconductor devices, and accordingly various measures have been taken on packages incorporating semiconductor chips. And a further downsizing of semiconductor devices has become possible by adopting a package structure in which external terminals of wiring for a semiconductor chip are arranged on the bottom face of the package and spherical solder pieces are fitted to ends of the wiring to serve as electrodes. For example, as disclosed in Japanese Unexamined Patent Application Publication No. 2004-161886, WLCSP (Wafer Level Chip Size Package) type semiconductor devices with packages about the same size as semiconductor chips have been put to practical use.
FIG. 10 is a perspective view illustrating the structure of a conventional WLCSP type semiconductor device. FIG. 11 is a sectional view illustrating the structure of the conventional WLCSP type semiconductor device. As shown in FIGS. 10 and 11, the WLCSP type semiconductor device 100 has a semiconductor substrate (semiconductor chip) 111 that has an integrated circuit portion (not illustrated) formed on the top face (one surface) thereof, electrode pads 112 formed on the top face of the semiconductor substrate 111, a sealing resin layer 113 formed on the top face of the semiconductor substrate 111, column-shaped metal posts 114 provided on the top face of the electrode pad 112 with the top faces of the metal posts 114 exposed through the sealing resin layer 113, and solder balls (projecting electrodes) 115 formed on the top faces of the metal posts.
In this way, with the WLCSP type semiconductor device 100, it is possible to reduce the package size to the size of the semiconductor substrate (semiconductor chip) 111 by providing the solder balls 115 which serve as external terminals on the top faces of the metal posts 114, while protecting the top surface of the semiconductor substrate (semiconductor chip) ill with the sealing resin layer 113. Structured as described above, the WLCSP type semiconductor device 100 is directly mounted on an external board such as a printed circuit board 119.
FIG. 12 is a sectional view illustrating the structure of the WLCSP type semiconductor device mounted on a printed circuit board. While the semiconductor device 100 is mounted on the printed circuit board 119 by connecting together the solder balls 115 and conductive bumps 118 provided on the printed circuit board 119 such as a glass/epoxy board, the semiconductor device 100 and the printed circuit board 119 are electrically connected together via the solder balls 115 and the conductive bumps 118.
After mounting a semiconductor device with a package structure similar to that of the WLCSP type semiconductor device 100 described above on a printed circuit board 119, thermal expansion or thermal contraction may arise in the semiconductor substrate 111 and the printed circuit board 119 as a result of temperature change or the like. In this case, the deformation force resulting from a difference in the degree of thermal expansion or a difference in the degree of thermal contraction between the printed circuit board 119 and the semiconductor substrate 111 acts in a concentrated fashion on the solder balls 115 as projecting electrodes. For this reason, damage or breakage such as cracks 125 may develop in the solder balls 115 (in particular to the base part of the solder balls 115 where the solder balls 115 and the sealing resin layer 113 are in contact with or close to each other).